1. Field of the Invention
The present invention relates to an inkjet printer and a method of fabricating a head unit for ejecting droplets of ink in an inkjet manner.
2. Description of the Background Art
In an inkjet printer, a head having outlet groups each of which ejects fine droplets of ink is used and by tilting the arrangement direction of the outlet groups in the head toward a direction orthogonal to a movement direction of the head relative to printing paper (i.e., a scan direction of the head), it is possible to change the resolution of an image to be written. Japanese Patent Application Laid Open Gazette No. 6-286140 (Document 1), Japanese Patent Application Laid Open Gazette No. 2003-305832 (Document 2) and Japanese Patent Application Laid Open Gazette No. 2002-113849 (Document 3), for example, disclose a technique in which a row of outlets which are aligned is tilted toward a direction orthogonal to a scan direction of a head and an ejection control of ink is performed for each of the outlets, to perform image writing at a high resolution, and Japanese Patent Application Laid Open Gazette No. 10-81015 (Document 4) discloses a technique in which a plurality of outlet rows each of which is tilted are arranged in a scan direction of a head, to perform image writing at a higher resolution. Japanese Patent Application Laid Open Gazette No. 2003-159786 (Document 5) discloses a technique in which a plurality of heads are arranged in a direction orthogonal to a scan direction of the heads with an arrangement direction of outlet groups tilted, to perform image writing in a wider range of printing paper with one scan.
On the other hand, another type of inkjet printer is well known, in which a plurality of heads are provided in a head unit and four outlet rows each having outlets disposed in a direction orthogonal to a scan direction (for example, at a pitch corresponding to 360 dpi (dot per inch)) are arranged along a scan direction in each head. In this printer, inks of four colors, i.e., K (black), C (cyan), M (magenta) and Y (yellow), are assigned to the four outlet rows in each head and a plurality of heads are disposed in two-row staggered arrangement along a direction orthogonal to the scan direction, to perform color printing at a resolution of 360 dpi on entire printing paper with one scan. In a case of color printing at a resolution of 720 dpi, two more rows of heads, like the two rows of heads for 360 dpi, are arranged in a direction orthogonal to the scan direction with half pitch shifted.
Further, Japanese Patent Application Laid Open Gazette No. 10-337862 discloses a technique for easily attaching a plurality of heads to a printer, in which a plurality of heads are fixed, being positioned, onto a holder and further fixed to a head unit body through the holder.
The techniques discloses in Documents 1 to 5, which are based on the premise that an ejection timing of ink is controlled for each outlet, need a complicate ejection control. In the color printer having the above head unit, for increasing the resolution, it is necessary to perform a high-level position adjustment for a plurality of heads in two respective directions corresponding to the scan direction and the direction orthogonal thereto and therefore fabrication of the head unit is not easy.